When the serial port is configured to “No Flow Control,” only Transmit, Receive, and Ground connections are required. Pin 7 and Pin 8 need to be connected only if other serial flow control types are selected.

If connecting to a 25 pin serial port on the computer, we suggest using a 9 to 25 pin serial adapter. The pin outs on a 25 pin serial port are not the same as a 9 pin port. When the serial port is configured to “No Flow Control”, only Transmit, Receive, and Ground connections are required. Request to Send and Clear to Send connections will need to be connected only if other serial flow control types are selected.

Pin 6 is connected only between multiple Whozz Calling? units and acts as a control line. When units are not transmitting data this line resides at -9 VDC. Upon transmit, the unit pulls this line to +9 VDC. Other Whozz Calling? units connected will detect this as a busy condition and will not transmit until the line returns to -9 VDC.

If your application program is designed to perform software controlled real time call blocking/passing it is important that the Pin 6 control line is at the very least, monitored for the busy condition. Since units cannot transmit and receive data at the same time, any commands that are issued by the software must be sent while units are not transmitting. The best solution is to monitor the control line on Pin 4 and pull it high with Pin 6 when your software is transmitting. This method will assure that commands sent to units will get through. This line should be pulled high by your serial port through a standard 1N4148 diode as diagrammed below.